1. Field of the Invention
The present invention relates to an electric wire connection structure adapted to connect a covered electric wire to a terminal and simultaneously assemble a housing having these members accommodated therein by the use of ultrasonic waves.
2. Description of Relevant Art
There is disclosed in Japanese Patent Publication No. 7-70345 a technique of applying ultrasonic vibration as a conventional technique for bringing a core wire of a covered electric wire and a terminal into mutual electric conduction therebetween as they are without uncovering an insulating covering thereof and simultaneously performing this electric conduction and the assembly of a relevant housing.
FIGS. 1A and 1B show a connector which is manufactured by this conventional technique and a first member 1 and a second member 2 each moded by resin oppose each other.
In an upper surface of the first member 1 there are longitudinally formed groove portions 3, and small concave portions 4 are formed in the longitudinal direction of the groove portion 3 at suitable intervals. Into the groove portion 3 of the first member 1 there is inserted in the longitudinal direction a terminal 5 on which a covered electric wire 6 is placed. The covered electric wire 6 is placed on the terminal 5 in a state where a number of core wires are covered by an insulating covering.
On an underside of the second member 2 there are longitudinally formed protruding portions 7 which are to be fitted into the groove portions 3 of the first member 1, and there are also formed small convex portions 8 which are to be fitted into the concave portions 4 of the groove portion 3.
This structure is assembled as follows. In a state where the terminal 5 and the covered electric wire 6 have been inserted into the groove portion 3, the protruding portion 7 of the second member 2 is fitted into the groove portion 3 of the first member 1, whereby the terminal 5 and the covered electric wire 6 are pressed by the second member 2 and the first member 1. At this time, at the portions wherein the concave portions 4 and the convex portions 8 are interfitted, the terminal 5 is partially bent to thereby prevent the terminal 5 and the covered electric wire 6 from being drawn off.
And, with the first member 1 and the second member 2 being clamped, ultrasonic vibration is applied from a horn (not shown). By the heat generated due to the vertical vibration applied by application of ultrasonic vibration, an insulating covering of the covered electric wire 6 is molten and splashed and thereby removed, with the result that a core wire of the covered electric wire 6 and the terminal 5 are brought into electric conduction therebetween. Simultaneously with this electric conduction, the first member 1 and the second member 2 are welded and integrated together, with the result that there is formed a housing having the terminal 5 and the electric wire accommodated therein, whereby a connector can be manufactured.
FIG. 2 shows a conventional structure for manufacturing a connector. A plurality of groove portions 3 are formed in a first member 1 and a plurality of protruding portions 7 which oppose the groove portions 3 are formed on a second member 2. And, a terminal is accommodated in each groove 3 and a covered electric wire is placed on this terminal, after which the resulting laminate is pressed by the first member 1 and the second member 2 and ultrasonic vibration is applied to the resulting structure in the identical way as mentioned above to thereby provide a connector.
However, the conventional structure involves therein the problem that contact between the terminal and the covered electric wire is likely to become insufficient. FIG. 3 is a section illustrating this. When connecting the terminal 5 and the core wire 9 of the covered electric wire 6 to each other, the heat generated due to the application of ultrasonic vibration causes thermal expansion of the protruding portion 7 of the second member 2 and a bottom wall portion 10 of the groove portion 3 of the first member 1. However, in natural cooling after the connection, the protruding portion 7 shrinks in a direction indicated by an arrow A and the bottom wall portion 10 of the groove portion 3 shrinks in a direction indicated by an arrow B which is opposite to the direction indicated by the arrow A. Due to this shrinkage made in the mutually opposite directions, the pressure of contact of the core wire 9 with the terminal 5 becomes low with the result that excellent contact between the core wire 9 and the terminal 5 becomes impossible with the result that the electric conduction between the two becomes defective and thus the reliability of the connection becomes low.
Such being the case, it is considered to form the first member 1 and the second member 2 by the use of the resin having a small coefficient of linear expansion which is less expanded and shrunk. However, that resin is less expanded and shrunk necessarily means that the shrinkage of resin is small at the time of molding thereof. Therefore, after the molding, the releasability thereof from the mold is inferior. For this reason, the molding of a member having the groove portions and protruding portions 7 which is of a configuration having a significantly large depth becomes difficult and therefore this technique is not practical. Besides, the resin having a small coefficient of linear expansion is expensive, which causes remarkable increase in cost of the completed product.